[Rails] Factorybot で生成したレコードが DB に保存されない

コード

describe "foo" do
  context "bar" do
    let(:post) { create(:post) }
    it "something" do
      # some request
      resp = Post.find(post.id)
      expect(resp.id).to eq(post.id)
      # => false
      # post.id
      # => nil
    end
  end
end

なぜか

let in RSpec is lazy loading. instance is not actually created until you reference it
ruby on rails - RSpec, Factory Girl and Capybara: no items saved - Stack Overflow

どう回避するか

use let! which is not lazy loading
ruby on rails - RSpec, Factory Girl and Capybara: no items saved - Stack Overflow

let はいつ使うか

ruby - When to use RSpec let()? - Stack Overflow (和訳)